Photo Sensor

ABSTRACT

A photo sensor has an insulator layer for covering a diode stack, and the insulator layer is made of photoresist to reduce a side leakage current.

RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/122,151, filed on May 16, 2008 and entitled “A Photo Sensor and aMethod for Manufacturing Thereof,” which claimed priority to TaiwanApplication Serial Number 96136414, filed Sep. 28, 2007, which areherein incorporated by reference.

BACKGROUND

1. Field of Invention

The present invention relates to a method of manufacturing asemiconductor device. More particularly, the present invention relatesto a method of manufacturing a photo sensor.

2. Description of Related Art

A “Sensor” detects heat, light or magnetic fields and converts thedetected physical parameter into electronic signals. By using the signalgenerated by the sensor, the user can obtain information therefrom.

According to the above, the data can be produced by a photo sensor thatgenerates a current with light. The photo sensor can be divided into twoparts, a transistor and a diode. The mechanism of the photo sensor isthat the light is directed to the diode to generate a current, and thenthe current is amplified from tens to hundreds of times to produce astronger signal.

However, in the conventional structure of the photo sensor, the materialof the insulating layer used to cover the diode usually is siliconnitride, silicon oxide, or silicon oxy-nitride. Nevertheless, thesematerials cannot provide good insulation. In addition, since both sidesof the diode are easily oxidized into silicon monoxide, the diode coveris degraded and current leakage from the diode through the insulatinglayer occurs. Furthermore, the conventional material for the insulatinglayer cannot provide good flatness. Therefore, there is a need todevelop a photo sensor to prevent current leakage and to improve theelectrical property of the photo sensor.

SUMMARY

The present invention provides a method of manufacturing a photo sensorto simplify the conventional process.

It is therefore an objective of the present invention to provide amethod of manufacturing a photo sensor. First, a substrate having aswitching element region and an electronic element region is provided.Next, a gate is formed on the switching element region of the substrate.A gate dielectric layer, a semiconductor layer, and an electricalproperty enhancement layer are formed in sequence to cover the gate andthe substrate. After that, the electrical property enhancement layer andthe semiconductor layer are patterned to form a channel region on thegate dielectric layer above the gate. Then, a first conductive layer, aplurality of element function layers and a second conductive layer areformed in sequence to cover the gate dielectric layer and the channelregion. Next, the second conductive layer and the element functionlayers are patterned wherein the element function layers patterned forma diode stack on the first conductive layer of the electronic elementregion, and the second conductive layer patterned forms aphoto-electrode on the diode stack. Furthermore, the first conductivelayer is patterned to form a source/drain above the opposite sides ofthe channel region and expose a part of the electrical propertyenhancement layer. Then, an insulating layer is formed to cover thesource/drain, the diode stack and the photoelectrode wherein thematerial of the insulating layer is a photoresist. The insulating layeris patterned to form an opening in the insulating layer and the openingexposes the photoelectrode. Moreover, a third conductive layer is formedto cover the insulating layer and the photoelectrode. Finally, the thirdconductive layer is patterned so that the third conductive layerpatterned covers a part of the insulating layer above the source/drainand connects to one side of the photoelectrode near the source/drainalong the opening.

It is another an objective of the present invention to provide a photosensor having at least one switching element region and an electronicelement region on a substrate. The photo sensor comprises a gate, a gatedielectric layer, a channel region, a source/drain, a diode stack, aphotoelectrode, a insulating layer and a bias electrode. The gate isdisposed on the switching element region of the substrate. The gatedielectric layer covers the gate and the substrate. The channel regionis disposed on the gate dielectric layer above the gate. Thesource/drain is disposed on the opposite sides of the channel region andcovers the gate dielectric layer underneath the opposite sides of thechannel region. The diode stack is disposed on at least one of thesource/drain in the electronic element region. The photoelectrode isdisposed on the diode stack. The insulating layer covers thesource/drain, the channel region, the diode stack and thephotoelectrode, and has an opening to expose a part of thephotoelectrode on the diode stack, wherein the material of theinsulating layer is a photoresist. The bias electrode is disposed on apart of the insulating layer on the source/drain and connects to oneside of the photoelectrode near the source/drain along the opening.

In the foregoing, compared with the conventional materials such assilicon nitride, silicon oxide or silicon oxynitride used for theinsulating layer, the insulating layer made of resin has betterinsulating effect and less current leakage. Meanwhile, since theinsulating layer made of resin can provide better flatness, the surfaceof the substrate becomes smoother and this is helpful for the laterprocess.

It is to be understood that both the foregoing general description andthe following detailed description are by examples, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a cross section view of a photo sensor according to oneembodiment of the present invention;

FIGS. 2A-2J illustrate cross section views of the photo sensor of FIG. 1at each manufacturing stage;

FIG. 3 illustrates a cross section view of the photo sensor having aprotective layer according to another embodiment of the presentinvention; and

FIG. 4 illustrates the results of the current leakage test for threedifferent diodes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

Refer to FIG. 1. FIG. 1 illustrates a cross section view of a photosensor according to one embodiment of the present invention. As show inFIG. 1, the photo sensor 100 is arranged on a substrate 102 which can bedivided into a switching element region 102 and an electronic elementregion 104. The photo sensor 100 comprises a gate 108, a gate dielectriclayer 110, a channel region 112, a source/drain 114, a diode stack 116,a photo electrode 118, a insulating layer 120 and a bias electrode 122.The gate 108 is disposed on the switching element region 104 of thesubstrate 102 and the gate dielectric layer 110 covers the gate 108 andthe substrate 102. The channel region 112 is disposed on the gatedielectric layer 110 above the gate 108, and comprises a semiconductorlayer 126 and an electrical property enhancement layer 128 disposed onboth sides of the semiconductor layer 126. The source/drain 114 isdisposed on the electrical property enhancement layer 128 of the channelregion 112 and covers the gate dielectric layer 110 underneath thechannel region 112.

A diode stack 116 is arranged on one of the source/drain 114 in theelectronic element region 106 of the substrate 102 and thephotoelectrode 118 is disposed on the diode stack 116. The insulatinglayer 120 covers the source/drain 114, the channel region 112, the diodestack 116 and both sides of the photoelectrode 118, and has a opening124 to expose a part of the photoelectrode 118 on the diode stack 116.The bias electrode 122 is disposed on a part of the insulating layer 120on the source/drain 114 and connects to one side 118 a of thephotoelectrode 118 near the source/drain 114 along the opening 124.

Next, FIG. 2A to FIG. 2J illustrate cross section views of the photosensor 100 of FIG. 1 described above at each manufacturing stage. Asshown in FIG. 2A, a substrate 102 is provided first, wherein thesubstrate 102 has a switching element region 104 and an electronicelement region 106. Next, a gate metal layer (not shown) is formed onthe substrate and then patterned to form a gate 108 on the switchingelement region 104 of the substrate 108. The substrate 102 is atransparent substrate, such as a glass substrate or a plastic substrate.The method used to form the gate metal layer can be physical vapordeposition, and the material used can be for example Mo, Cr, an alloy ofMo and Cr, an alloy of Mo and W, the complex material of Mo—Al—Mo or thecomplex material of Cr—Al—Cr. The thickness of the gate metal layer isbetween 2000 Å and 4000 Å.

Refer to FIG. 2B, a gate dielectric layer 110, a semiconductor layer126, and an electrical property enhancement layer 128 are formed insequence on the gate 108 and the substrate 102. The method used to formthese three layers can be chemical vapor deposition wherein thethickness of the gate dielectric layer is between 2500 Å and 4000 Å andis made of silicon nitride. The thickness of the semiconductor layer 126is between 4000 Å and 1500 Å and the material thereof is amorphoussilicon. The thickness of the electrical property enhancement layer 128is between 1000 Å and 100 Å and the material is doped silicon.

Refer to FIG. 2C, the electrical property enhancement layer 128 and thesemiconductor layer 126 are patterned to form a channel region 112 onthe gate dielectric layer 110 above the gate 108.

After that, Refer to FIG. 2D, a first conductive layer 107, a pluralityof element function layers 116 a, 116 b, 116 c and a second conductivelayer 117 are formed in sequence on the gate dielectric layer 110 andthe channel region 112. The element function layers 116 a, 116 b and 116c are a first doping layer, an intrinsic semiconductor layer, and asecond doping layer, respectively. In the embodiment, the method used toform the element function layers 116 a, 116 b and 116 c can be chemicalvapor deposition. The element function layer 116 a is an n-doped siliconlayer with thickness between 250 Å and 500 Å. The element function layer116 b layer is an amorphous silicon layer with thickness between 4500 Åand 8000 Å. The element function layer 116 c layer is a p-doped siliconlayer with thickness between 110 Å and 200 Å. However, in theembodiment, the element function layers 116 a and 116 c are used asexemplified, which can also be p-doped silicon layer and n-doped siliconlayer, respectively. The first conductive layer 107 and the secondconductive layer 117 can be formed by physical vapor deposition whereinthe first conductive layer 107 can be metal, such as copper or the alloythereof, with thickness between 2000 Å and 4000 Å. The second conductivelayer 117 is made of a transparent material, such as indium tin oxide,aluminium zinc oxide, indium zinc oxide, cadmium zinc oxide or thecombination thereof, with thickness between 300 Å and 500 Å. In thefollowing process described, the first conductive layer 107 and theelement function layer 116 a-116 c will further form a source/drain anda diode stack, respectively.

Refer to FIG. 2E, the second conductive layer 117 and the elementfunction layers 116 a-116 c are patterned so that the element functionlayers 116 a-116 c turns into a diode stack 116 on the first conductivelayer 107 of the electronic element region 106, and the secondconductive layer 117 becomes a photoelectrode 118 on the diode stack116. Since the photo electrode 118 is made of transparent material,light can directly pass through the photo electrode 118 and then to thediode stack 116 to generate a current, while using the photo sensor 110.In addition, according to the materials used for the element functionlayers 116 a-116 c, it is known that the diode 116 is a PIN diodewherein an amorphous silicon layer is arranged between a p-doped siliconlayer and a n-doped silicon layer so that the enlarged depletion regioncan generate a greater current after being illuminated.

Refer to FIG. 2F, the first conductive layer 107 is patterned to form asource/drain 114 above the opposite sides of the channel region 112 andexpose a part of the electrical property enhancement layer 128. Theelectrical property enhancement layer 128 in the channel region 112reduces the resistance between the semiconductor layer 126 and thesource/drain and 114 to enhance the Ohmic Contact property. The OhmicContact property is that the contact resistance between two differentmaterials is small and steady, which will not change as the voltage ischanged. Since there is a difference between the energy level of theamorphous silicon material used for the semiconductor layer 126 and thatof the metal used for the source/drain 114, this results in increasingthe resistance. Therefore, by arranging a high doped electrical propertyenhancement layer 128 between the semiconductor layer 126 and thesource/drain 114, electrons can flow between the metal and thesemiconductor material much more easily so that the Ohmic Contactproperty can be improved. Similarly, in the embodiment of the presentinvention, the Ohmic Contact property between the element function layer116 b and the first conductive layer 107, and between the elementfunction layer 116 b and the photoelectrode 118 can be improved by theelement function layers 116 a (an n-doped silicon layer) and the elementfunction layers 116 c (a p-doped silicon layer), respectively.

Refer to FIG. 2G, after patterning the first conductive layer 107 iscompleted, the electrical property enhancement layer 128 is selectivelyetched to expose a part of the semiconductor layer 126.

Next, refer to FIG. 2H, an insulating layer 120 is formed to cover thesource/drain 114, the channel region 112, the diode stack 116 and thephotoelectrode 118. After that, the insulating layer 120 is patterned toform an opening 124 in the insulating layer 120 so that a part of thephotoelectrode 118 is exposed. In the embodiment, the thickness of theinsulating layer 120 is between 0.5 μm and −1.6 μm and can be made ofcommon photoresists, such as phenolic resin, or black matrix photoresist(e.g., the photoresist comprises epoxy resin (Novolac), acrylic resin,etc.). Compared with the conventional material used, such as siliconnitride, silicon oxide, or silicon oxynitride, in this embodiment, theinsulating layer 120 made of resin not only provides good impedanceability but also forms better coverage on the side of the diode stack116 so that the generation of the leakage current can be decreased.

Refer to FIG. 2I, the third conductive layer 121 is formed on the secondconductive layer 117 in the opening 124 and the insulating layer 120.The thickness of the third conductive layer 121 is between 2000 Å- and4000 Å and the material used is metal, such as copper.

Refer to FIG. 2J, the third conductive layer 121 is patterned so thatthe third conductive layer 121 patterned forms a bias electrode 122. Asshown in FIG. 2J, the bias electrode 122 covers a part of the insulatinglayer 120 above the source/drain 114 and connects to one side 118 a ofthe photoelectrode 118 near the source/drain 114 along the opening 124.The bias electrode 122 not only provides a bias voltage for the diodestack 126, but also is an effective shield against the light.

Furthermore, refer to FIG. 3. FIG. 3 illustrates a cross section view ofthe photo sensor 100 according to another embodiment of the presentinvention. In the embodiment, to provide sufficient protection for thephoto sensor 100, a protective layer 123 is formed to cover theinsulating layer 120, the bias electrode 122 and the photoelectrode 118.Then, the protective layer 123 is patterned so that the protective layer123 patterned covers the bias electrode 122 and the insulating layer 120in the electronic element region 106, and a lighting opening 130 isformed above the diode stack 116 to expose a part of the photoelectrode118. In the embodiment, the material used for the protective layer 123depends on the insulating layer 120. For example, while the materialused for the insulating layer 120 is resin type black matrix photoresisthaving light shielding function, the protective layer 123 can be made ofcommon photoresist without light shielding function or resin type blackmatrix photoresist with light shielding function. While the material ofthe insulating layer 120 is common photoresist without light shieldingfunction, the material used for the protective layer 123 needs to bemade of resin type black matrix photoresist with light shieldingfunction to provide better light shield effect.

To examine whether the photo sensor manufactured by the process abovecould prevent the leakage current or not, a bias voltage is applied tothree kinds of PIN diodes to test the leakage of the current. Thesethree kinds of PIN diodes tested are: (1) PIN diode without aninsulating layer; (2) PIN diode with a conventional silicon nitrideinsulating layer; and (3) PIN diode with a epoxy resin insulating layer.The result is shown in FIG. 4.

Refer to FIG. 4. FIG. 4 illustrates the results of the current leakagetest for three different diodes. As shown in FIG. 4, the PIN diodewithout an insulating layer has the greatest leakage current, which is7.45×10⁻⁹ per unit area (500 μm×500 μm). The conventional PIN diode witha silicon nitride insulating layer has a less leakage current,1.23×10⁻¹¹ per unit area. As to the PIN diode with an epoxy resininsulating layer, it has the fewest leakage current, only 3.4×10⁻¹³,which is decreased at least 40% compared with that of the conventionaldiode.

According to above, compared with the conventional materials such assilicon nitride, silicon oxide or silicon oxynitride used for theinsulating layer, the insulating layer made of resin has betterinsulating effect so that the leakage current can be reduced. Meanwhile,since the insulating layer made of resin can provide better flatnessthan other materials (e.g., silicon nitride), the surface of thesubstrate will become smoother and this is helpful for the laterprocess.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A photo sensor having at least one switching element region and anelectronic element region on a substrate, wherein the photo sensorcomprises: a gate disposed on the switching element region of thesubstrate; a gate dielectric layer covering the gate and the substrate;a channel region disposed on the gate dielectric layer above the gate; asource/drain disposed on the opposite sides of the channel region andcovering the gate dielectric layer underneath the opposite sides of thechannel region; a diode stack disposed on at least one of thesource/drain in the electronic element region; a photoelectrode disposedon the diode stack; a insulating layer covering the source/drain, thechannel region, the diode stack and the photoelectrode, and having aopening to expose a part of the photoelectrode on the diode stack,wherein the material of the insulating layer is a photoresist; and abias electrode disposed on a part of the insulating layer on thesource/drain and connecting to one side of the photoelectrode near thesource/drain along the opening.
 2. The photo sensor of claim 1, whereinthe photoresist is resin type black matrix photoresist.
 3. The photosensor of claim 1, wherein the photoresist is phenolic resin, epoxyresin, or acrylic resin.
 4. The photo sensor of claim 1, wherein thethickness of the insulating layer is at least 0.5 μm.
 5. The photosensor of claim 1, wherein the thickness of the insulating layer is0.5-1.6 μm.
 6. The photo sensor of claim 1, further comprising aprotective layer disposed on the bias electrode and the insulating layerof the electronic element region, and having a lighting opening toexpose a part of the photoelectrode.
 7. The photo sensor of claim 1,wherein the channel region comprises: a semiconductor layer; and anelectrical property enhancement layer disposed on both sides of thesemiconductor layer.
 8. The photo sensor of claim 7, wherein theelectrical property enhancement layer is an n-doped silicon layer. 9.The photo sensor of claim 1, wherein the diode stack comprises a firstdoping layer, an intrinsic semiconductor layer, and a second dopinglayer.
 10. The photo sensor of claim 9, wherein the first doping layeris an n-doped silicon layer and the second doping layer is a p-dopedsilicon layer.
 11. The photo sensor of claim 9, wherein the intrinsicsemiconductor layer is an amorphous silicon layer.